CN112844073A - Polytetrafluoroethylene composite membrane with three-dimensional supporting structure - Google Patents

Abstract

The invention discloses a polytetrafluoroethylene composite membrane with a three-dimensional support structure, which is characterized in that after specific thermoplastic resin is added into PTFE dispersion resin, the thermoplastic resin can form a microporous structure in the longitudinal and transverse stretching processes, the thermoplastic resin is longitudinally and transversely interwoven with micro-fibers in a PTFE microporous membrane, and the upper layer and the lower layer of the thermoplastic resin are mutually connected in the expanding process of the PTFE microporous membrane, so that the composite membrane not only has a support effect in the PTFE microporous membrane, but also has the advantages of reducing the pore diameter of the PTFE microporous membrane and controlling the pore structure due to the existence of the composite microporous structure, improving the porosity, the mechanical property and the stability of the expanding structure, and when the composite membrane is hot-pressed and compounded with a base material, the melting point of the thermoplastic resin is lower, the composite membrane can be melted at low temperature, the self-bonding effect is realized, the ventilation loss and the mechanical damage in the membrane covering process are reduced, the membrane fastness is improved, and the service life of a product, shortens the process route and reduces the environmental pollution and the production cost.

Description

Polytetrafluoroethylene composite membrane with three-dimensional supporting structure

Technical Field

The invention relates to a polytetrafluoroethylene composite membrane with a three-dimensional support structure and a preparation method thereof, belonging to the technical field of membrane preparation.

Background

Expanded polytetrafluoroethylene microporous membrane (e-PTFE) is widely applied to the fields of air filtration, water filtration and clothing, but the Polytetrafluoroethylene (PTFE) membrane produced industrially at present has the defects of large pore diameter, low porosity, insufficient mechanical property and the like. The current process for preparing the PTFE microporous membrane mainly comprises the following steps: the PTFE microporous membrane prepared by the technology has the defects of low porosity, large aperture, uncontrollable property, poor mechanical property and the like, thereby limiting the application field of the PTFE microporous membrane.

On the other hand, when the PTFE microporous membrane is used in the field of air filtration, the PTFE microporous membrane needs to be compounded with a base material, before the air filtration, the base material is firstly subjected to chemical treatment to improve the compounding fastness of the PTFE microporous membrane and the base material, but the air permeability of a product and the mechanical property of a filter layer can be obviously reduced when the method is adopted for high-temperature hot-pressing compounding, so that the service life of the product is shortened, the chemical treatment process causes certain pollution to the environment, the production cost is increased, and the production efficiency is reduced.

In order to solve the above problems, patent CN111408284A adds other fluorine-containing thermoplastic resin to PTFE dispersion resin, and improves the uniformity and mechanical properties of the pore structure by reshaping the microporous structure, but has the following disadvantages: the PTFE microporous membrane prepared by the method has an uncontrollable pore structure, requires higher temperature when being subjected to hot-pressing compounding with a base material, increases the ventilation loss and the mechanical loss of the PTFE microporous membrane, and reduces the service life of a product. According to the invention, the thermoplastic resin with the rigid characteristic is added into the PTFE dispersion resin, and in the process of biaxial stretching, the thermoplastic resin can also form a microporous structure, is interwoven with the microfiber-node of the PTFE microporous membrane, and connects the upper layer and the lower layer of the expanded PTFE microporous membrane together to play a supporting role, so that the PTFE composite membrane has good mechanical property, high porosity, uniform and controllable pore structure and stable expanded structure through the three-dimensional support structure.

Disclosure of Invention

The invention aims to provide a polytetrafluoroethylene composite membrane with a three-dimensional support structure and a preparation method thereof.

The above object of the invention is achieved by the features of the independent claims, the dependent claims developing the features of the independent claims in alternative or advantageous ways.

In order to achieve the above purpose, the present invention provides a polytetrafluoroethylene composite membrane with a three-dimensional support structure and a preparation method thereof, comprising the following steps:

(1) mixing PTFE dispersion resin, thermoplastic resin with hard elastic characteristic and surfactant according to a certain mass ratio, adding extrusion aid after uniformly mixing, uniformly mixing again, and then carrying out aging treatment on the mixture;

(2) extruding and rolling the mixture treated in the step (1) to obtain a composite rolled belt containing thermoplastic resin;

(3) and (3) degreasing the composite calendered tape obtained in the step (2), and then performing a biaxial stretching process, high-temperature sintering and cooling to prepare the PTFE composite film with the three-dimensional support structure.

Preferably, in the step (1), the thermoplastic resin is any one or a combination of several of Polyamide (PA), poly 4-methyl-1 pentene (PMP), Polyethylene (PE), polypropylene (PP), and the like, and in order to further ensure the excellent performance and uniformity of the PTFE composite film, the thermoplastic resin is preferably any one or two of Polyethylene (PE) and polypropylene (PP); the thermoplastic resin accounts for 5-30wt% of the mixture.

Preferably, in the step (1), the extrusion aid is any one or a combination of more of gasoline, aviation kerosene, naphtha, petroleum ether and the like, and accounts for 5-20wt% of the mixture.

Preferably, in the step (1), the aging treatment temperature is 25-50 ℃ and the time is 12-36 h.

Preferably, in order to improve the uniformity of mixing the PTFE dispersion resin and the thermoplastic resin, the PTFE dispersion resin and the thermoplastic resin are mixed in a mass ratio, and a surfactant is added, wherein: the surfactant accounts for 1-10wt% of the mixture.

Preferably, in the step (2), the extrusion head during extrusion is a circular or flat die, the compression ratio is 5-120, and the flat die is preferred to ensure the uniformity of the micropore and microfiber-node distribution of the PTFE composite film.

Preferably, in the step (2), the distance between two press rolls in the rolling process is 50-400 μm, the roll speed is 1-20m/min, and the temperature of the press rolls is 30-90 ℃.

Preferably, in the step (3), the degreasing temperature before stretching is 100-; the biaxial stretching process is asynchronous stretching or synchronous stretching, wherein: when the asynchronous stretching process is adopted, longitudinal stretching is firstly carried out, and then longitudinal and transverse stretching is carried out, wherein the stretching temperature is 150-350 ℃, the longitudinal stretching multiplying power is 5-25, and the transverse stretching multiplying power is 5-25; in order to further ensure the consistency of the distribution of the microfiber-node of the PTFE composite membrane, a synchronous stretching process is preferred, namely, the composite membrane is stretched longitudinally and transversely at the same time, wherein the stretching temperature is 150-350 ℃, the longitudinal stretching magnification is 5-25, and the transverse stretching magnification is 5-25.

Preferably, in the step (3), the temperature during the high-temperature sintering is 327-.

Compared with the prior art, the invention has the beneficial effects that:

(1) after the specific thermoplastic resin is added into the PTFE dispersion resin, the thermoplastic resin can form a microporous structure in the longitudinal and transverse stretching processes, and is longitudinally and transversely interwoven with the microfibers in the PTFE microporous membrane, and the upper layer and the lower layer of the PTFE microporous membrane are also connected with each other in the expanding process of the PTFE microporous membrane, so that the PTFE microporous membrane not only plays a supporting role, but also reduces the aperture of the PTFE microporous membrane and has controllable pore structure due to the existence of the composite microporous structure, and the porosity, the mechanical property and the stability of the expanding structure are improved.

(2) When the obtained PTFE microporous composite film and the base material are subjected to hot-pressing compounding, the specific thermoplastic resin in the PTFE composite film has a lower melting point, can be melted at low temperature, plays a role in self adhesion, reduces the air permeability loss and the mechanical damage during film covering, increases the film covering fastness, prolongs the service life of products, shortens the process route, and reduces the environmental pollution and the production cost.

It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the presently disclosed subject matter unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.

The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description taken in conjunction with the accompanying drawings. Additional aspects of the present invention, such as features and/or advantages of exemplary embodiments, will be apparent from the description which follows, or may be learned by practice of specific embodiments in accordance with the teachings of the present invention.

Drawings

FIG. 1 is a process flow diagram of a PTFE composite membrane with a three-dimensional support structure according to the present invention.

Detailed Description

In order to better understand the present invention, the following examples are further provided to illustrate the present invention, but the present invention is not limited to the following examples.

Embodiments of the invention are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.

The conception of the invention is as follows: in the invention, the specific thermoplastic resin in the PTFE dispersion resin can form a microporous structure in the process of biaxial stretching, is longitudinally and transversely interwoven with the microfibers in the PTFE microporous membrane, and can connect the upper layer and the lower layer with each other in the process of expanding the PTFE microporous membrane, so that the specific thermoplastic resin not only plays a supporting role in the PTFE microporous membrane, but also reduces the aperture of the PTFE microporous membrane and has controllable pore structure due to the existence of a composite microporous structure, thereby improving the porosity, the mechanical property and the stability of the expanded structure.

All of the starting materials of the present invention, without particular limitation as to their source, may be purchased commercially or prepared according to conventional methods well known to those skilled in the art.

The surfactants referred to in the following examples all used sodium dodecylbenzenesulfonate.

The molecular weight of the PTFE dispersion resin in the following examples is preferably 800-1200 ten thousand, and the crystallinity is preferably 95% or more.

The filtration efficiency tests described in the following examples and comparative examples used a dust filtration efficiency test system, the equipment type being Filteq FEMA 1-AT, Germany AT ambient temperature, in accordance with the standards VDI/DIN 3926, ASTM D6830-02, ISO 11057, GB/T6719, GB12625, the test dust being standard dust.

Example 1

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and poly 4-methyl-1 pentene (PMP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture to perform high-speed mixing after the uniform mixing, and performing aging treatment after the uniform mixing, wherein: PMP resin accounts for 10wt% of the mixture, petroleum ether accounts for 15 wt% of the mixture, surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The PTFE composite membrane obtained by the process has the thickness of 13.5 mu m, the pore size of 1.267 mu m, the porosity of 88.6 percent, the maximum force of 7.6N when the warp direction breaks and the elongation at break of 123.8 percent, the maximum force of 5.9N when the weft direction breaks and the elongation at break of 154.4 percent, and the air permeability of 7.4 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 230 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 5.6cm/s, and the filtering efficiency is 99.927.

Example 2

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and polypropylene (PP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the PP resin accounts for 10wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The PTFE composite membrane obtained by the process has the thickness of 12.4 mu m, the pore size of 1.026 mu m, the porosity of 90.7%, the maximum force of warp-wise fracture of 8.9N, the elongation at break of 133.7%, the maximum force of weft-wise fracture of 6.5N, the elongation at break of 165.3% and the air permeability of 7.8 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 165 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 6.8cm/s, and the filtering efficiency is 99.958.

Example 3

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and Polyethylene (PE) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the PE resin accounts for 10wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of the high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The thickness of the PTFE composite membrane obtained by the process is 13.1 mu m, the pore size is 0.997 mu m, the porosity is 91.2%, the maximum force when the warp direction breaks is 9.7N, the breaking elongation is 142%, the maximum force when the weft direction breaks is 7.1N, the breaking elongation is 169.7%, and the air permeability is 7.5 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 130 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 6.9cm/s, and the filtering efficiency is 99.975.

Example 4

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and polypropylene (PP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the PP resin accounts for 5 wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The PTFE composite membrane obtained by the process has the thickness of 14.1 mu m, the pore size of 1.355 mu m, the porosity of 91.9 percent, the maximum force of 7.5N when the warp direction breaks and the elongation at break of 128.3 percent, the maximum force of 5.4N when the weft direction breaks and the elongation at break of 155.7 percent, and the air permeability of 8.8 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 165 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 7.6cm/s, and the filtering efficiency is 99.923.

Example 5

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and polypropylene (PP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the PP resin accounts for 30wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The thickness of the PTFE composite membrane obtained by the process is 9.2 mu m, the pore size is 0.981 mu m, the porosity is 92.8%, the maximum force when the warp direction breaks is 9.4N, the elongation at break is 145.5%, the maximum force when the weft direction breaks is 8.1N, the elongation at break is 177.6%, and the air permeability is 7.2 cm/s. When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 165 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 6.7cm/s, and the filtering efficiency is 99.998.

Comparative example 1

Referring to FIG. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure of the present invention, which is described by referring to CN111408284A, comprises the following steps in sequence:

(A) mixing PTFE dispersion resin and Fluorinated Ethylene Propylene (FEP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the FEP resin accounts for 10wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The thickness of the PTFE composite membrane obtained by the process is 13.1 mu m, the pore size is 1.224 mu m, the porosity is 88.6%, the maximum force when the warp direction breaks is 6.7N, the breaking elongation is 121.3%, the maximum force when the weft direction breaks is 4.3N, the breaking elongation is 149.6%, and the air permeability is 6.2 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 275 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane filter material with high air permeability, filter efficiency, low resistance and high membrane fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 4.1cm/s, and the filtering efficiency is 97.698.

Referring to patent CN111408284A, when FEP resin is added in the present invention, the PTFE composite membrane has large pore size, low porosity and low air permeability, and when the PTFE composite membrane is compounded with a glass fiber fabric substrate, a high temperature process is required, the air permeability of the compounded filter material is low, the air permeability loss of the composite membrane is high, and the filtration efficiency is low.

Comparative example 2

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and polypropylene (PP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the PP resin accounts for 2 wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The PTFE composite membrane obtained by the process has the thickness of 16.9 mu m, the pore size of 1.492 mu m, the porosity of 89.6 percent, the maximum force of 6.9N when the warp direction breaks and the elongation at break of 120.9 percent, the maximum force of 5.2N when the weft direction breaks and the elongation at break of 151.3 percent, and the air permeability of 7.2 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 165 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 5.1cm/s, and the filtering efficiency is 98.241.

Comparative example 3

Referring to fig. 1, the method for preparing a PTFE composite membrane with a three-dimensional support structure according to the present invention includes the following sequential steps:

(A) mixing PTFE dispersion resin and polypropylene (PP) resin in a high-speed mixer, adding a surfactant into the mixture to improve the mixing uniformity of the two resins, adding an extrusion aid (petroleum ether) into the mixture after the mixture is uniformly mixed, and performing aging treatment after the mixture is uniformly mixed, wherein: the PP resin accounts for 40 wt% of the mixture, the petroleum ether accounts for 15 wt% of the mixture, the surfactant accounts for 5 wt% of the mixture, the rotating speed of a high-speed mixer is 45r/min, the mixing time is 25min, the aging temperature is 50 ℃, and the aging time is 48 h.

(B) Extruding the treated mixture by a flat die extrusion head, wherein the compression ratio is 96, the temperature of a calendering roller is 30 ℃, the distance between the two rollers is 250 mu m, the roller speed is 6m/min, and the obtained composite calendering belt has the thickness of 300 mu m and the width of 260 mm;

(C) degreasing the composite rolled belt at 150 ℃, synchronously stretching longitudinally and transversely at 290 ℃, 18 longitudinal stretching multiplying power and 20 transverse stretching multiplying power, and finally sintering at 380 ℃ and cooling at a cooling rate of 5 ℃/min to obtain the PTFE composite membrane with the three-dimensional support structure. The PTFE composite membrane obtained by the process has the thickness of 8.1 mu m, the pore size of 0.904 mu m, the porosity of 93.5 percent, the maximum force of 8.1N when the warp direction breaks and the elongation at break of 131.0 percent, the maximum force of 6.5N when the weft direction breaks and the elongation at break of 153.1 percent, and the air permeability of 6.1 cm/s.

When the prepared PTFE composite membrane and the glass fiber woven fabric are subjected to hot-pressing compounding, the selected hot-pressing temperature is 165 ℃, the pressure is 0.2MPa, and the vehicle speed is 10m/mim, the glass fiber cloth membrane-covered filter material with high air permeability, high filtering efficiency, low resistance and high membrane-covering fastness is prepared, and the test result shows that: the air permeability of the glass fiber cloth membrane filter material is 4.3cm/s, and the filtering efficiency is 99.996.

TABLE 1 tabulation of the process parameters for each of the examples and comparative examples

TABLE 2 List of key Performance parameters for each example and comparative example

The specific technological parameters of the implementation can adopt corresponding technological parameters according to different plastic resins with hard characteristics. Adding other thermoplastic resins into the PTFE dispersion resin for blending modification, such as: polyamide (PA), poly-4-methyl-1 pentene (PMP), Polyethylene (PE), polypropylene (PP), and the like. Through the addition of other thermoplastic polymers, when the PTFE membrane is subjected to biaxial stretching, the thermoplastic polymers are firstly melted between the nodes of the PTFE and then stretched into fibers, micro fibers in the PTFE microporous membrane are longitudinally and transversely interwoven together, and the upper layer and the lower layer are also connected with each other in the expanding process of the PTFE membrane to play a supporting role, so that the aperture of the PTFE microporous membrane is reduced, and the porosity, the mechanical property and the stability of an expanded structure are improved. On the other hand, when the PTFE microporous membrane and the base material are subjected to hot-pressing compounding, the thermoplastic resin in the PTFE composite membrane is melted, so that the self-adhesion effect is achieved, the process route is shortened, and the environmental pollution and the production cost are reduced.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims (10)

1. A preparation method of a polytetrafluoroethylene composite membrane with a three-dimensional support structure is characterized by comprising the following steps:

(1) mixing PTFE dispersion resin and thermoplastic resin according to a certain mass ratio, adding an extrusion aid after uniformly mixing, uniformly mixing again, and then aging the mixture;

(2) extruding and rolling the mixture treated in the step (1) to obtain a composite rolled belt containing thermoplastic resin;

(3) and (3) degreasing the composite calendered belt obtained in the step (2), and then sequentially carrying out biaxial tension, high-temperature sintering and cooling to prepare the PTFE composite membrane with the three-dimensional support structure.

2. The method of claim 1, wherein the thermoplastic resin is any one or a combination of polyamide, poly-4-methyl-1 pentene, polyethylene and polypropylene.

3. The method of claim 1, wherein the thermoplastic resin is either one or both of polyethylene and polypropylene.

4. The method of claim 1, wherein in step (1), the thermoplastic resin is present in an amount of 5 to 30wt% based on the mass of the compounded material.

5. The method according to claim 1, wherein in the step (1), the extrusion aid is any one or a combination of gasoline, aviation kerosene, naphtha and petroleum ether, and the extrusion aid accounts for 5-20wt% of the mixture.

6. The method according to claim 1, wherein in the step (1), the PTFE dispersion resin and the thermoplastic resin are mixed in a mass ratio, and a surfactant is added, wherein the surfactant accounts for 1 to 10wt% of the mixture.

7. The method of claim 1, wherein in step (2), the extrusion head during extrusion is a round or flat die with a compression ratio of 5-120.

8. The method as claimed in claim 1, wherein in the step (3), the degreasing temperature before stretching is 100-350 ℃; the biaxial stretching process is asynchronous stretching or synchronous stretching, wherein when the asynchronous stretching process is adopted, longitudinal stretching is firstly carried out, and then longitudinal and transverse stretching is carried out, the stretching temperature is 150-350 ℃, the longitudinal stretching magnification is 5-25, and the transverse stretching magnification is 5-25; when the synchronous stretching process is adopted, the stretching temperature is 150-350 ℃, the longitudinal stretching magnification is 5-25, and the transverse stretching magnification is 5-25.

9. The method as claimed in claim 1, wherein in the step (3), the temperature during the high temperature sintering is 327 ℃ and 400 ℃, and the cooling rate is 1-50 ℃/min.

10. A polytetrafluoroethylene composite membrane having a three-dimensional support structure made by the method of any one of claims 1-9.

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